In metalcutting machine tools, it is frequently necessary and desirable to provide a device for containing the metal chips within an enclosed environment in order to prevent chip contamination of precision machine ways, keep operator walkways clean, render chip cleanup in an easier fashion, etc.
In relatively small machine tools, for example, that depicted in U.S. Pat. No. 5,181,898, of T. W. Piotrowski, Jan. 26, 1993, entitled Cover Assembly for Multi-Configurable Machine Tool, a totally enclosed rigid guarding system is provided for the machine. On still older types of machine tools, for example, manually controlled knee mills, it has been known to use an operator shield or sheet metal panel which may be stood up at the edge of a machine table to deflect errant metal chips back onto the table.
In very large machine tools, for example, stack routers and profilers used in the aircraft industry, the problem of chip containment becomes more acute. The reasons for this include the fact that the workholding base of the machine is extremely long, a typical bed length being in the magnitude of forty to fifty feet, and the motorized spindle head, which drives multiple spindles and cutting tools, traverses the full length of the bed. Further, the workpieces are often aluminum, and the free cutting, lightweight chips are projected far from the workpiece.
Because of the length of travel involved, consideration of machine guarding to assist in chip containment within the machine confines naturally directs a designer to consider an extensible guard which can expand and collapse according to the direction of cutter travel. Consideration of extensible guarding leads one to consider curtains which may be folded and extended much like a shower curtain, and bellows-type guarding wherein sewn or molded discrete bellows sections are joined serially to create a long accordion-like extensible guard.
In a machine tool such as a multi-axis profiler, the work surface and slide movement is generally in a horizontal direction, thus necessitating a relatively thin vertical curtain which tends to be very flimsy and must be adequately supported to keep from falling over.
It has been well-known in the bellows art to provide clinched grommets spaced along the bellows length, where the grommets are fitted over a stationary rod so the bellows may hang and ride in a straight line as it is horizontally expanded or contracted. The rod solution does not lend itself to extremely long extensible guards, because of the sag involved and the difficulty in placing any rod support intermediate of the rod ends.
U.S. Pat. No. 4,278,352, of B. E. Keller, Jul. 14, 1981, entitled Support System for Extensible Bellows, teaches an apparatus for supporting a horizontally extended bellows which encloses a light beam in an optical interferometer, wherein one end of the bellows is attached to a relatively stationary support while the other end of the bellows is relatively movable and is attached to a movable slide. The bellows is fitted with a plurality of spaced grommets along each side, and a pair of side cables are threaded through the grommets in a generally horizontal fashion. One end of a cable is attached to the slide while the other end of the cable is tensioned by the following means:
(a) in one embodiment, the cable extends over a pulley to a vertical attitude, and a weight is hung on the end of the cable to keep tension and thereby horizontally support the bellows; and PA1 (b) an alternative embodiment discloses that the tension producing end of the cable be attached to a spring-loaded take-up spool which will tend to wind the cable as the slide moves toward the take-up spool. As the slide moves away from the take-up spool, the cable always remains taut.
Several difficulties inherent in the '352 patent device prevent its use in a machine tool which has extremely long horizontal travel. In the first embodiment, the gravity device provides no adjustment for the tension force. The vertical travel of the tensioning weight is the same as the horizontal movement, and machine tools of the type described are not configured to have a slide elevation which permits this vertical travel. In the second embodiment, the spring-wound spool is not capable of maintaining a substantially constant tension force in the cable as the slide is moved over an extremely long travel, since, although the spring mechanism is not detailed in the '352 patent, most springs have a linear relationship in their load-to-travel ratio; this also applies to torsion springs. The '352 patent device imparts an unbalanced load to the slide, and a widely fluctuating unbalanced load may seriously affect slide position.
The present invention obviates the foregoing difficulties of the '352 patent in a novel manner.